Chemical Mechanical Polishing or Planarization (CMP) is a planarization method used in the semiconductor industry and in other industries such as the optical and flat panel polishing industries, which typically involves removal of material by a combination of relatively gentle abrasion of the layer being planarized (e.g. a Si wafer coated with a metal or dielectric layer) by a polishing pad (composed of a polymer or other relatively soft material) in the presence of a chemically active slurry. The slurry typically contains abrasive nano-particles in colloidal suspension and a reactive chemical agent (e.g. an oxidizer, such as hydrogen peroxide for planarizing metal layers) whose reaction with the planarizing layer is facilitated by the mechanical action of the abrasive particles and a polishing pad typically designed in a particular structure or within a range of roughness. During the CMP process, the surface of the polishing pad may be gradually saturated with polishing nanoparticles, polishing debris and portions of abraded pad material, thus potentially increasing the contact area to an extent that modifies the removal rate of the planarizing material and/or increases the rate of defects of the planarization process through scratching of various sizes. In addition, the polishing pad surface can be abraded leading to a less controlled polishing process of the substrate being removed. Thus to perform a controlled and effective planarization process, these abrasive particles may need to be periodically removed from the polishing pad surface and the pad surface regenerated to a desired surface roughness and rate of defects. Such an action may be accomplished using a conditioning disk or CMP pad conditioner. Due to the hardness of typical abrasive particles and to increase its practical lifetime, the conditioning disk is often fabricated of a hard material, such as diamond. The uniformity and reproducibility of the CMP process often depends on the uniformity and reproducibility of the conditioning process.
Simple conditioning disks often use diamond grit (diamond particles of size from a few microns to a few tens of microns, selected by sieving though filters with different mesh sizes) incorporated into a metal layer (typically formed by electroplating). Such disks may have a Gaussian distribution of diamond particle sizes with a typical standard deviation of 15-20% of the maximum grit size. If, for a given applied force during the pad conditioning process, the penetration depth of the grit into the pad is less than 2-3 standard deviations of the grit height, a substantial number of grit particles (possibly less than 3%) may not touch the pad at all, thus leading to large variations in the uniformity of the pad conditioning process. Metal embedded diamond grit particles can also loosen and fall off, generating scratches or other defects on the substrates that are being planarized.
To overcome these problems and to lengthen effective work life, some conditioning disk manufacturers use CVD diamond to embed larger diamond particles, which are typically screened to reduce the distribution of their sizes. The extent of improvement can be measured, for example, by the number of wafers that can be processed with the same pad, which typically increases from 250 to 300 for the superior CVD diamond-embedded conditioners. However, for a range of applications, such as damascene and double damascene technologies, and as feature dimensions for silicon process technology continue to shrink in the sub-100 nm range, even such improved conditioning technology may still be prone to limitations imposed by irreproducibility in CMP removal rates and pad lifetime. Another issue with these embedded grit pads is that during the wear process of the conditioners, some of the embedded diamond particles may break or be dislodged. Since they might be quite large (e.g. 10-50 μm) hard diamond particles, they can be a significant source of defects on wafers as they are known to cause large scratches on polishing surfaces which can cause failure or reliability problems with surfaces polished by the pads being conditioned.
U.S. Pat. No. 6,076,248 describes a micro-structured surface with individually “sculpted” abrasive regions arranged in irregular arrays. It is primarily directed at the manufacture of a “master tool” for the preparation of other abrasives. It describes the individual sculpting of each abrasive region, i.e. many individual sculpting events. It does not describe a diamond abrasive structure (or diamond geometrical protrusion) covered surface.
U.S. Pat. No. 5,152,279 describes an abrasive surface with abrasive particles embedded in a surface in a roughly predetermined manner. U.S. Pat. No. 5,107,626 describes the method of using the abrasive article of U.S. Pat. No. 5,152,279 to provide a patterned surface. U.S. Pat. No. 6,821,189 describes a similar abrasive to the previous two patents but it also includes a diamond-like carbon coating. These patents do not discuss a method to tightly control the size and placement of the geometrical protrusions (sometimes referred to as “grit” in these various abrasive patents), on the surface.
US patent application 20050148289 describes CMP micromachining. It describes flexible polishing pads to aid in micromachining. Such polishing pads may benefit from embodiments presented here, both in terms of precision and in length of work life.
U.S. Pat. No. 7,410,413 describes another method of creating an abrasive article including the formation of “close-packed pyramidal-shaped composites”. This abrasive patent discusses the mixing and formation of a composite of abrasives and a binder. This patent does not describe the exact placement of each geometrical protrusion. Neither does it describe methods to select in advance or design a placement location, shape and size for each geometrical protrusion.